JP2001223008A - Lithium secondary battery, positive electrode active substance for it and their manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a homogeneous and substituted lithium cobalt complex oxide which is not only superior in a cycle property, but also gives a secondary battery of a high capacity, and moreover superior in thermal stability, and provide its manufacturing method. SOLUTION: The substituted lithium cobalt complex oxide expressed in an equation Lix My Co1-y Oz is provided (in the equation, M is at least one kind of metallic element selected among Al, Ti, Mn, Mo and Sn, and x is a number ranging from 0.8 to 1.2, and y is a number ranging from 0.001 to 0.10). The oxide is used as a positive electrode active substance of a lithium secondary battery. By mixing powders of lithium compound, cobalt compound, and a compound of the element M so that the molar ratio agrees with the equation (I) in lower aliphatic alcohol of a carbon number 1-3, drying it, and calcining it at a temperature ranging from 600 to 1,100 deg.C under the oxidizing atmosphere, the substituted lithium cobalt complex oxide can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery, a positive electrode active material comprising a lithium-cobalt composite oxide therefor, and a method for producing the same. More specifically, the present invention relates to a lithium-ion secondary battery having a lithium-cobalt composite oxide containing a substitution element as a positive electrode active material, and having improved cycle characteristics and thermal stability. It relates to oxides and a simple and economical method for producing them.

[0002]

2. Description of the Related Art In recent years, against the background of miniaturization and high performance of electronic equipment, a lithium-ion secondary battery having a light weight, a high voltage, a high energy density and a long service life has been developed as a power source therefor. Demand is increasing rapidly, and research on the practical application of lithium-ion secondary batteries in the field of electric vehicles and large-scale power storage devices is also being conducted in order to cope with the global decline in resources and environmental degradation. It is being energetically advanced.

Conventionally, a lithium cobalt composite oxide (LiCoO) has been used as a positive electrode active material of a lithium ion secondary battery.
₂ , lithium cobalt oxide) is widely used because it has a high voltage of 4V class and a high energy density. But,
Lithium-ion secondary batteries using lithium-cobalt composite oxide as a positive electrode active material lose their crystal structure and lose their function as an active material during repeated charging and discharging.
Cycle characteristics are not enough. Further, in such a battery, since the lithium-cobalt composite oxide decomposes at a temperature of about 200 ° C., when abnormal heat generation such as an internal short circuit occurs, the battery may be damaged, and in a high temperature environment, There is a problem that the cycle characteristics are significantly deteriorated and the thermal stability is lacking.

[0004] In view of the above, a substituted lithium-cobalt composite oxide in which a part of cobalt atoms in the lithium-cobalt composite oxide is replaced with another element to suppress a change in crystal structure due to the charge and discharge described above is provided. However, it has been conventionally proposed.

However, heretofore, such a substituted lithium cobalt composite oxide has been disclosed in, for example, Japanese Patent Application Laid-Open No. 3-201368.
JP, JP-A-4-319259, JP-A-5-2
As described in US Pat. No. 83075 and the like, necessary raw material powders, for example, lithium carbonate and cobalt carbonate are dry-mixed with an oxide of a substitution element, and the mixture is fired in the air, then cooled and pulverized. It is manufactured by.

According to such a dry method, that is, a method utilizing a solid phase reaction using the raw material powder as a reactant, it is inherently difficult to obtain a uniform mixture of the raw material powder at a submicron level. In order to obtain a practicable composite oxide by firing such a mixture of the raw material powders, it is actually necessary to use a relatively large amount of the raw material powder of the substitution element, It is necessary to carry out pulverization and further to repeat such calcination and pulverization so that the desired solid phase reaction is sufficiently performed. However, on the other hand, if the raw material powder containing a large amount of the compound of the substitution element is repeatedly fired at a high temperature as described above, undesirable by-products may be generated or the surface properties of the reaction product may be changed in an undesirable manner. In addition to
A battery using the obtained composite oxide as a positive electrode active material has a small battery capacity, and thus cannot provide a composite oxide that provides a battery having excellent characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional substituted lithium cobalt composite oxide as a positive electrode active material for a lithium ion secondary battery, Aims to provide a homogeneous substituted lithium-cobalt composite oxide having not only excellent cycle characteristics but also a high capacity secondary battery, and also excellent thermal stability, and a method for producing the same.
It is an object to provide a lithium ion secondary battery using such a substituted lithium cobalt composite oxide as a positive electrode active material.

[0008]

According to the present invention According to an aspect of the general formula _{Li x M y Co 1-y} O 2 (I) ( wherein, M is at least Al, Ti, Mn, selected from Mo and Sn X represents 0.8 to 1.
2 is a number in the range of 2, and y is a number in the range of 0.001 to 0.10. The present invention provides a substituted lithium cobalt composite oxide for use as a positive electrode active material of a lithium ion secondary battery.

According to the present invention, such a substituted lithium-cobalt composite oxide is prepared by mixing a powder of a lithium compound, a cobalt compound and a compound of an element M in an aliphatic lower alcohol having 1 to 3 carbon atoms in terms of the molar ratio of the elements. It can be obtained by mixing so as to conform to the general formula (I), drying this, and firing it in an oxidizing atmosphere at a temperature in the range of 600 to 1100 ° C.

Further, according to the present invention, there is provided a lithium ion secondary battery using such a substituted lithium cobalt composite oxide as a positive electrode active material.

[0011]

Lithium-cobalt composite oxide for use as positive active material for a lithium ion secondary battery according to the embodiment of the present invention have the general formula _{Li x M y Co 1-y} O 2 (I) ( wherein, M Represents at least one metal element selected from Al, Ti, Mn, Mo, and Sn, and x is 0.8 to 1.0.
2 is a number in the range of 2, and y is a number in the range of 0.001 to 0.10. ), Wherein part of the cobalt atom is replaced by the above-described element M (hereinafter, referred to as a substitution element).

In the substituted lithium cobalt composite oxide represented by the general formula (I), x is preferably 0.9.
~ 1.1, particularly preferably 1.
Is in the range of 0.002 to 0.075, more preferably in the range of 0.005 to 0.05, and particularly preferably
It is in the range of 0.01 to 0.03.

In the lithium-cobalt composite oxide represented by the general formula (I), when y is smaller than 0.001, the obtained composite oxide has almost no improvement in cycle characteristics and thermal stability. , Y is greater than 0.10, the resulting composite oxide has improved cycle characteristics, but the battery capacity is significantly reduced.

In particular, according to the present invention, the replacement element is preferably at least one element selected from Ti and Mn in view of excellent initial discharge capacity, cycle characteristics and thermal stability. , Ti. For example, by using titanium as a substitution element, a small amount, for example, 0.5 to 5 mol% (that is, when y is 0.5 to 0.5 mol%).
005-0.05), preferably 1-3 mol% (i.e.
By replacing y with 0.01 to 0.03), the initial discharge capacity,
A composite oxide for a secondary battery positive electrode active material having excellent cycle characteristics and thermal stability can be obtained.

According to the present invention, such a substituted lithium-cobalt composite oxide is obtained by converting a powder of a lithium compound, a cobalt compound and a compound of a substitution element in an aliphatic lower alcohol having 1 to 3 carbon atoms into a molar ratio of elements. And the above general formula (I)
And dried under an oxidizing atmosphere at 600 to 1100 ° C., preferably 700 to 100 ° C.
It can be obtained by firing at a temperature in the range of 0 ° C.

In the method of the present invention, lithium hydroxide, lithium oxide, lithium carbonate, organic acid salts (eg, formate, oxalate, acetate, etc.) are used as the lithium compound. However, lithium carbonate or lithium hydroxide is preferably used. On the other hand, oxides, hydroxides, oxyhydroxides, carbonates, nitrates, sulfates, chlorides, and the like are usually used as the cobalt compound and the compound of the substitution element. object,
Organic acid salts and the like are preferably used. These lithium compounds, cobalt compounds and compounds of the substitution elements are all used in powder form, but are not particularly limited in their particle size.

According to the method of the present invention, firstly, a substituted lithium-cobalt composite oxide for the purpose _{Li x M y Co 1-y} O
_In a molar ratio for producing ₂ , a lithium / cobalt compound / substituted element compound powder adjusted to a required Li / M / Co molar ratio is added to a solvent composed of an aliphatic lower alcohol having 1 to 3 carbon atoms, Mix in this solvent. According to the present invention, x is the number 1 in the range of 0.8 to 1.2, as described above. Therefore, according to the present invention, a composite oxide having a stoichiometric atomic ratio is also provided. A composite oxide having a non-stoichiometric atomic ratio can be obtained in a similar manner.

Examples of the aliphatic lower alcohol include methanol, ethanol, n-propanol and isopropanol. Of these, methanol is particularly preferred. Methanol as this solvent preferably does not contain water, but may contain water in a range of 20% by weight or less.

In the present invention, by using the aliphatic lower alcohol as a solvent and mixing the raw material powder in the solvent, the particles of the compound of the substitution element can be substantially reduced to the primary particle level in the mixture. Can be uniformly dispersed.

The amount of the solvent used is not particularly limited, but is preferably such that a paste is formed when a lithium compound, a nickel compound, and a powder of a compound of a substitution element are mixed in the solvent. I just need.

Next, according to the present invention, after heating and drying such a paste, the paste is heated in an oxidizing atmosphere such as air at 600 to 1100 ° C., preferably 700 to 1100 ° C.
00 ° C, most preferably at a temperature in the range of 750-950 ° C, for a relatively short period of time, usually 0.5-10 ° C.
By firing for a time, preferably about 0.5 to 5 hours, the desired substituted lithium-cobalt composite oxide can be obtained.

According to the present invention, this composite oxide has a primary particle size in the range of 0.5 to 5 μm and a secondary particle size in the range of 1 to 30 μm so as to have excellent battery characteristics. Is preferred.

According to the present invention, as described above, a mixture of the raw material powders is obtained as a paste, which is dried and then fired. Can be used, for example, using a microwave heating device at 100 to 350 ° C.
After heating to a temperature in the range described above and drying, the mixture is continuously fired at a temperature of 600 to 1000 ° C. using an electric furnace as described above, whereby the target composite oxide can be obtained quickly. . Of course, heating and baking of the paste may be performed using a microwave heating device.

According to the present invention, a mixture of the above raw material powders is obtained as a paste, which is dried, and then dried in a rotary kiln under an oxidizing atmosphere at a temperature of 700 to 1000.
C., preferably by heating to a temperature in the range of 750 to 950.degree. As described above, when a rotary kiln is used, a substituted lithium-cobalt composite oxide having excellent cycle characteristics can be obtained usually by firing for one hour or less.

According to the present invention, cycle characteristics and thermal stability are markedly improved by using a lithium-cobalt composite oxide obtained by substituting a part of cobalt atoms with another element M as a positive electrode active material. Thus, an improved lithium secondary battery can be obtained. In particular, according to the present invention, the cycle characteristics and thermal stability can be significantly improved by substituting the cobalt atoms with preferably 5 mol% or less of the substitution elements, as mentioned above, ,
By mixing a lithium compound and a cobalt compound in a compound powder of the substitution element in the alcohol solvent,
It is considered that the compound powder of the substitution element can be dispersed in the raw material powder at a level of substantially primary particles.

The lithium ion secondary battery according to the present invention
A positive electrode, a negative electrode made of a carbonaceous material capable of occluding and releasing lithium, a lithium alloy or lithium ions, a separator disposed between the positive electrode and the negative electrode, and a lithium ion conductive nonaqueous (organic) electrolyte. including. Such a lithium ion nonaqueous secondary battery is already well known.

For example, when the positive electrode is used in a coin-type battery, a positive electrode active material, a conductive agent and a binder are mixed, and this mixture (positive electrode mixture) is pressure-formed to form a disc. A positive electrode can be obtained. As the conductive agent, for example, graphite is used, and as the binder, for example, polytetrafluoroethylene or the like is used. On the other hand, the negative electrode is made of a carbonaceous material capable of occluding and releasing lithium metal, a lithium alloy or lithium ions, and has a shape of
It is determined appropriately according to the positive electrode. Further, the positive electrode and the negative electrode may be used together with a current collector, if necessary.

As the separator provided between the positive electrode and the negative electrode, for example, a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene, a porous film made of a polyolefin, or the like is used.

As the lithium ion conductive organic electrolyte, for example, an electrolytic solution obtained by dissolving an electrolyte in a non-aqueous solvent is preferably used, but is not limited to this. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone,
Sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and the like are used. These are used alone or as a mixture of two or more.

Examples of the lithium ion conductive electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and lithium arsenide hexafluoride (LiAsF).
₆ ), lithium trifluoromethanesulfonate (LiC
F ₃ SO ₃ ), lithium aluminum chloride (LiAlC)
l) and the like. Such an electrolyte is usually used in the non-aqueous solvent so as to have a concentration of 0.5 to 1.5 mol / L.

Further, in the present invention, instead of using the combination of the organic electrolyte solution and the separator as described above, a lithium ion conductive solid electrolyte which also serves as the separator can be used. Various types of such solid electrolytes are already known.

FIG. 1 shows an example of a coin-type lithium secondary battery. That is, in this battery, for example, a positive electrode current collector 2 is disposed on the bottom surface of a positive electrode can 1 made of stainless steel, a disk-shaped positive electrode 3 is laminated thereon, and further, The separator 4 is laminated. The disk-shaped negative electrode 5 is provided on the separator, and the negative electrode current collector 6 is provided on the negative electrode. Further, the negative electrode can 7
A negative electrode can 7 having the negative electrode current collector on the bottom surface is provided via an insulating packing 8 so as to liquid-tightly seal the opening of the positive electrode can. The negative electrode can 7 is made of, for example, stainless steel. Further, the lithium ion conductive electrolyte is usually impregnated and supported on a separator.

[0033]

According to the present invention, the compound of the substitution element can be dispersed almost as primary particles by mixing the raw material powder in the solvent comprising the alcohol,
Thus, it is possible to easily obtain a raw material mixture obtained by uniformly dispersing the compound of the substitution element, and further, after drying this mixture, baking at a predetermined temperature in an oxidizing atmosphere for a relatively short time, The intended substituted lithium cobalt composite oxide can be obtained. That is, according to the method of the present invention, unlike the conventional dry method, high-quality and high-performance composite oxides can be easily obtained by firing at a lower temperature for a shorter time without repeating firing and pulverization. Can be obtained.

In addition, according to the lithium ion secondary battery using the composite oxide as a positive electrode active material, the lithium ion secondary battery has a high voltage of 4V class, a high energy density, and excellent charge / discharge cycle characteristics. Excellent thermal stability.

[0035]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

Example 1 Lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃
O ₄ ) and titanium dioxide (TiO ₂ ) by Li / (Co +
Ti) the molar ratio is 1.0, y = Ti / (Co + Ti)
Mixing and stirring were performed in methanol such that the molar ratio became 0.005, 0.01, 0.03, or 0.10 to obtain a paste. After the paste was dried by heating, it was fired in an electric furnace at 900 ° C. for 3 hours in the air to obtain a titanium-substituted lithium-cobalt composite oxide LiTi _y Co _1-y O ₂ .

The titanium-substituted lithium core thus obtained
85 weight parts of Baltic composite oxide, 10 weight graphite as conductive agent
Parts and polytetrafluoroethylene 5 weight as binder
Parts of the mixture into a positive electrode mixture, which is press-formed and disc-shaped.
Was prepared. Disc-shaped lithium used as negative electrode
Was. In addition, the electrolytic solution is composed of ethylene carbonate and diethyl carbonate.
Phosphorus hexafluoride was added to a mixture of 1: 2 by volume of carbonate.
Lithium oxide (LiPF ₆ ) At a concentration of 1 mol / L
Prepared. Microporous polypropylene as separator
Using a film, the coin-shaped test type shown in Fig. 1
A secondary battery was assembled.

This battery was charged at 25 ° C. at a current density of 1 mA / cm ^{2 to an} upper limit voltage of 4.3 V, and discharged at a current density of ² mA / cm ^{2 to a} lower limit voltage of 3.0 V. The charge / discharge was repeated to examine the cycle characteristics of the discharge capacity. Table 1 shows the replacement ratio of cobalt atoms by titanium atoms and the retention of discharge capacity at 150 cycles of a lithium ion secondary battery using the obtained composite oxide. The discharge capacity retention rate was (discharge capacity at 150 cycles (V) / initial discharge capacity (V)) × 1008.
(%). FIG. 2 shows the relationship between the number of cycles and the discharge capacity. A to E in FIG.
Corresponds to A to E in the middle.

[0039]

[Table 1]

Next, a titanium-substituted lithium-cobalt composite oxide L in which 1 mol% of the above cobalt atoms are substituted with titanium is used.
A battery having iTi _0.01 Co _0.99 O ₂ as a positive electrode active material and a battery having an unsubstituted lithium-cobalt composite oxide LiCoO ₂ as a positive electrode active material were fully charged (charging conditions: 3 hours at a current of 1 C, 4.3 V). After that, the positive electrode was taken out of each battery, washed with diethyl carbonate, and dried in vacuum.

Lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / L in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 to prepare an electrolytic solution, which was added to the positive electrode. Then, DSC (differential scanning calorimetry) measurement was performed. The results are shown in FIG.

Unsubstituted lithium cobalt composite oxide Li
CoO_Two Positive electrode with an active material of DS
Sudden rise of C curve, that is, rapid heat generation
You. However, the titanium-substituted lithium cobalt according to the present invention
Composite oxide LiTi_0.01Co _0.99O_Two Positive as active material
At the pole, heat is generated from around 140 ° C
There is no sharp rise of the DSC curve
A crab peak is formed. Also, the peak of fever is high.
It has shifted to the warm side. Thus, the replacement resource according to the invention is
The positive electrode using the active material of titanium-cobalt composite oxide
Lithium cobalt composite oxide LiCoO_Two The active material
As compared with the positive electrode described above.

Example 2 Lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃
O ₄ ) and manganese acetate ((CH ₃ COO) ₂ Mn) have a Li / (Co + Mn) molar ratio of 1.0, and y = Mn /
Mixing and stirring were performed in methanol so that the (Co + Mn) molar ratio was 0.01, to obtain a paste. After the paste was dried by heating, it was dried in air using an electric furnace.
By calcining at 0 ° C. for 3 hours, a manganese-substituted lithium-cobalt composite oxide LiMn _0.01 Co _0.99 O ₂ was obtained.

In the above, aluminum oxide, molybdenum oxide or tin oxide is used in place of manganese acetate in an amount of 1 mol% with respect to each cobalt atom.
An aluminum, molybdenum or tin-substituted lithium cobalt composite oxide was obtained.

Using these substituted lithium-cobalt composite oxides, a coin-type lithium ion secondary battery for testing was assembled in the same manner as in Example 1, and the initial discharge capacity and the discharge at 70 cycles were similarly set. The capacity retention was examined. In addition, for the battery of Example 1 using the titanium-substituted lithium-cobalt composite oxide obtained in Example 1 as a positive electrode active material, the initial discharge capacity and the discharge capacity retention rate at 70 cycles were similarly examined. Table 2 shows the results. FIG.
Fig. 2 shows the relationship between the number of cycles and the discharge capacity of each battery. 4 correspond to a to f in Table 2, respectively.

[0046]

[Table 2]

Example 3 Lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃
O ₄ ) and titanium dioxide (TiO ₂ ) by Li / (Co +
Ti) the molar ratio is 1.0, y = Ti / (Co + Ti)
The mixture was mixed and stirred in methanol so that the molar ratio became 0.01, to obtain a paste. After the paste was dried by heating, it was baked at 900 ° C. for 45 minutes in the air using an electric furnace to obtain a titanium-substituted lithium-cobalt composite oxide Li.
Ti _0.01 Co _0.99 O ₂ was obtained.

A coin-type lithium ion secondary battery for testing was assembled in the same manner as in Example 1 except that a disk-shaped positive electrode was prepared using the titanium-substituted lithium-cobalt composite oxide thus obtained. When the characteristics of this battery were evaluated under the same conditions as in Example 1, the initial discharge capacity was 148.8 mAh / g, the discharge capacity at 100 cycles was 132.1 mAh / g, and the discharge capacity retention was 88.8. %Met.

Example 4 Lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃
O ₄ ) and titanium dioxide (TiO ₂ ) by Li / (Co +
Ti) the molar ratio is 1.0, y = Ti / (Co + Ti)
The mixture was mixed and stirred in methanol so that the molar ratio became 0.01, to obtain a paste. The paste was dried by heating, dried and pulverized. The obtained powder was placed in a rotary kiln, and heated and fired at 650 ° C., 750 ° C., 950 ° C. or 950 ° C. for 40 minutes in an air atmosphere. FIG. 5 shows an X-ray diffraction diagram of the fired product thus obtained. 75
It is shown that calcining at 0 ° C. for 40 minutes can obtain a titanium-substituted lithium-cobalt composite oxide LiTi _0.01 Co _0.99 O ₂ .

Next, the paste prepared from the above raw material powder was dried and pulverized in the same manner as described above, and the obtained powder was charged into a rotary kiln, and then dried under an air atmosphere at 775.
And baked at a temperature of 795 ° C. or 845 ° C. for 40 minutes to obtain a titanium-substituted lithium-cobalt composite oxide LiT
i _0.01 Co _0.99 O ₂ was obtained.

To 90 parts by weight of the titanium-substituted lithium-cobalt composite oxide, 4 parts by weight of graphite as a conductive agent and 6 parts by weight of polytetrafluoroethylene as a binder were mixed to form a positive electrode mixture. Thus, a disk-shaped positive electrode was prepared. Disc-shaped lithium was used as the negative electrode. Also,
The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / L in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 2. Using a microporous polypropylene film as a separator, a test coin-type lithium ion secondary battery shown in FIG. 1 was assembled.

This battery was repeatedly charged and discharged under the same conditions as in Example 1, and the cycle characteristics of the discharge capacity were examined. FIG. 6 shows the relationship between the number of cycles and the discharge capacity. As shown in FIG. 6, the discharge capacity retention of the lithium ion secondary battery using the titanium-substituted lithium-cobalt composite oxide obtained by firing at 775 ° C. as a positive electrode active material during 300 cycles was 81.5%. The firing temperature was 79.3% at 795 ° C., and the firing temperature at 845 ° C. was 77.5%.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a lithium ion secondary battery.

FIG. 2 is a graph showing the relationship between the number of cycles and the discharge capacity of a lithium ion secondary battery using a lithium cobalt composite oxide in which cobalt atoms are replaced with titanium at various ratios as a positive electrode active material.

FIG. 3 shows a titanium-substituted lithium cobalt according to the present invention.
Composite oxide LiTi_{0. 01}Co_0.99O_Two Positive as active material
Electrodes and unsubstituted lithium cobalt complex acids as comparative examples
LiCoO_Two And DS
It is a graph which shows a C curve.

FIG. 4 is a graph showing the relationship between the number of cycles and the discharge capacity of a lithium ion secondary battery using a lithium cobalt composite oxide obtained by substituting 1 mol% of cobalt atoms with various elements as a positive electrode active material. is there.

FIG. 5 is a diagram showing a process for producing a lithium-cobalt composite oxide obtained by substituting 1 mol% of cobalt atoms with titanium, drying a mixture paste of raw material powders, pulverizing the mixture, and sintering the mixture at various temperatures using a rotary kiln. 1 shows an X-ray diffraction diagram of the fired product obtained as described above.

FIG. 6 shows a titanium-substituted lithium-cobalt composite oxide LiTi _0.01 obtained by firing using a rotary kiln.
5 is a graph showing the relationship between the number of cycles and the discharge capacity of a lithium ion secondary battery using Co _0.99 O ₂ as a positive electrode active material.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode can, 2 ... Positive electrode collector, 3 ... Positive electrode, 4 ... Separator, 5 ... Negative electrode, 6 ... Negative electrode collector, 7 ... Negative electrode can, 8 ... Insulating packing.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiko Hirao 3-5-24-2 Miyahara, Yodogawa-ku, Osaka-shi Inside Honjo Chemical Co., Ltd. F-term (reference) in Honjo Chemical Co., Ltd. 4G048 AA04 AB02 AB05 AC06 AD03 AE05 5H029 AJ03 AJ14 AK03 AK07 AL12 AM03 AM04 AM05 AM07 BJ03 BJ16 CJ02 CJ28 DJ16 HJ02 HJ14 5H050 AA08 AA19 BA17 CA14

Claims (7)

[Claims] 1. A in the general formula _{Li x M y Co 1-y} O 2 (I) ( wherein, M represents Al, Ti, Mn, of at least one metal element selected from Mo and Sn, x is 0.8-1.
2 is a number in the range of 2, and y is a number in the range of 0.001 to 0.10. A substituted lithium-cobalt composite oxide for use as a positive electrode active material for a lithium ion secondary battery. 2. The substituted lithium cobalt composite oxide according to claim 1, wherein y is a number in the range of 0.002 to 0.05. 3. The substituted lithium cobalt composite oxide according to claim 1, wherein M is at least one element selected from Ti and Mn. Wherein in the general formula _{Li x M y Co 1-y} O 2 (I) ( wherein, M represents Al, Ti, Mn, of at least one metal element selected from Mo and Sn, x is 0.8-1.
2 is a number in the range of 2, and y is a number in the range of 0.001 to 0.10. The method for producing a positive electrode active material for a lithium ion secondary battery comprising a substituted lithium-cobalt composite oxide represented by the following formula): Are added so as to correspond to the above general formula in terms of the molar ratio of the elements, mixed, dried, and dried under an oxidizing atmosphere at 600.degree.
Baking at a temperature in the range of １1100 ° C. 5. The method according to claim 4, wherein the solvent is methanol. 6. The method according to claim 4, wherein the solvent is methanol containing water in a range of not more than 20% by weight. 7. A positive electrode, a negative electrode made of a carbonaceous material capable of occluding and releasing lithium, a lithium alloy or lithium ions, a separator disposed between the positive electrode and the negative electrode, and a lithium ion conductive non-aqueous A lithium ion nonaqueous secondary battery comprising: an electrolyte; and the active material of the positive electrode comprises the substituted lithium cobalt composite oxide according to claim 1.